1. Field of the Invention
This invention relates to well packers used in subterranean oil or gas wells and more specifically to retrievable well packers and well tool assemblies which can be set and released by manipulation of a tubular string, including application of a tensile or compressive force through the tubing string to set or release the packer.
2. Description of the Prior Art
Conventional packers used to seal the annulus between a tubing string and the casing in a subterranean oil or gas well can either be permanent packers or retrievable packers. Retrievable packers are intended to be lowered into the well bore and set at some desired downhole location to isolate the annular areas above and below the packer and between the inner and outer conduit during certain downhole operations. Retrievable packers, like permanent packers, employ a sealing or packing element to form the annular seal engaging both the casing and sealing along the exterior of the tubing string. Although not essential for simpler packers, more complex packers also employ means to anchor the packer in engagement with well casing. Conventionally, radially expandable anchoring slips having an exterior surface suitable for gripping the well casing are employed with more complex retrievable packers. Depending upon the conditions to be encountered in the subsurface well, packers may employ anchoring slips capable of holding the packer in place against only upwardly directed forces. Conversely, packers may employ anchoring slips capable of holding the packer in place against downwardly directed surfaces. However, in all but the simpler applications, packers must be anchored against forces acting in opposite directions. In many conventional retrievable packers, anchoring slips are expanded radially outwardly by oppositely facing expanders or cones or wedges which are axially shiftable to engage the lower surface of the anchoring slips. In conventional packers, means have been provided for expanding the packing element simultaneously with the expansion of the anchoring slips or expanding the packing before or after actuation of the anchoring slips.
Conventional retrievable packers and similar downhole tools can be actuated by fluid pressure, by wireline or by manipulation of the tubing string. Hydraulic or hydrostatic retrievable packers are commonly used in deviated wells where tubing manipulation cannot be reliably transmitted to the packer apparatus. Either rotational or longitudinal manipulation has been employed to set retrievable packers. Some retrievable packers have employed a combination of rotational and longitudinal manipulation or longitudinal force applied through the tubing string to set a packer. For example, the retrievable packer disclosed in U.S. Pat. No. 3,507,327 employs rotational manipulation and compressive force or set-down weight to maintain the packer in a set configuration. Other conventional packers, such as the model "AD-1" tension set packer shown on page 845 of the 1982-83 Composite Catalog of Oil Field Equipment And Services published by World Oil are set in response to a tensile force applied through the tubing.
In addition to merely manipulating the packers between a retracted and an expanded set configuration, longitudinal forces or stresses applied to the packer can be significant in maintaining an adequate seal over the life of the packer. Extrusion of the packing element can result in a loss of the longitudinal compressive stress necessary to maintain proper squeeze on the packing elements and a proper wedging action to the anchoring slips in expanded configuration. Therefore, it is desirable either to maintain a continuous axial force or stress on the packing element and slip assembly or to provide means for intermittently applying longitudinal stress to the packer assembly. In actual oil field operations, it is often simpler to apply a tensile force to the packing element, since adequate compressive forces may be difficult to apply.
Among the applications for which retrievable packers are employed are for production, water flooding, high pressure fracturing, acidizing, pumping, disposal, testing stimulation, workover or other operations. Use of packers in these operations impose certain performance requirements upon retrievable packers, as well as requirements imposed by various regulatory authorities. For example, regulatory authorities may require that a retrievable packer be capable of holding a prescribed pressure from both directions to provide an adequate safety margin. Furthermore, the use of other equipment with a packer, especially in view of the few ways in which downhole tools can be actuated, may impose further restrictions. For example, the use of a downhole shutoff valve, such as that disclosed in U.S. Pat. Nos. 4,270,606 or in 4,458,751 requires that rotational manipulation be transferred to a valve incorporated in the tubing string. The valves disclosed in those patents are actuated by rotational manipulation of the tubing string. Normally a packer is used to provide a reaction force to permit relative rotation between various components of the valves. It follows that only packers which can be set and released in a compatible manner can be used with valves of this type.
While numerous packers having one or a portion of capabilities of the tension set neutral packer disclosed in this application is known, none has all of the capabilities of the device disclosed herein.